Fibre-based packaging materials for containers and product packages, such as packaging paper or board, are usually provided with a polymeric coating that makes the material liquid-tight and allows forming the container or package by heat sealing. Typical articles made from polymer coated paper or board are liquid packages and disposable tableware, such as drinking cups. LDPE (low-density polyethylene) is widely used for coating due to its good heat-sealability.
Recently there has been a growing demand on the market for such paper or board products made solely or at least predominantly of raw-materials from renewable sources, i.e. raw-materials of biologic origin. Traditionally polyethylenes have been produced from fossile raw materials such as petroleum. More recently polyethylenes made from sugarcane, sugar beet or wheat grain have been developed, especially bio-LLDPE (linear low-density polyethylene) and bio-HDPE (high-density polyethylene) having easy availability. Also bio-LDPE, i.e. usual low-density polyethylene with a branched structure, is known but has limited supply and accordingly a high price. All these new polymer products have so far been tailored for the manufacture of polymer films, and their suitability to extrusion coating has been found to be poor.
EP 1 059 162 A2 describes packaging materials having layers of a blend of LDPE and LLDPE as a monolayer or as an innermost layer or an outermost layer of a multilayer coating on a paperboard base. The teachings principally aim at a liquid crystal polymer barrier, and there is no mention of the proportions of LDPE and LLDPE in the blend.
WO 00/776862 A1 discloses a monolayer of a blend of LDPE and LLDPE on a paperboard base, without teaching the proportions of the polymers in the blend. In this reference the principal teaching are focused to a polymer/nanoclay composite layer as an oxygen and moisture barrier.